Where is the attic air filter in my trane xr13?

Question

Where is the attic air filter in my trane xr13?

Answer 1

it may be in the house behind the return air duct grate.   that's the large one that sucks air in, not blowing out.  

Answer 2

Look for a return air vent in your house. Usually about 20'' x 30'' metal vent. There will be clips to open it . Your air filter will be behind it.